1. Field of the Invention
Embodiments of the present invention generally relate to a substrate storage cassette.
2. Description of the Related Art
Semiconductor substrate processing is typically performed by subjecting a substrate to a plurality of sequential processes to create devices, conductors and insulators on the substrate. Each of these processes are generally performed in a processing chamber configured to perform a single step of the production process. In order to efficiently complete the entire sequence of processing steps, a number of processing chambers are typically coupled to a central transfer chamber that houses a robot to facilitate transfer of the substrate between the processing chambers. A semiconductor processing platform having this configuration is generally known as a cluster tool, examples of which are the family of CENTURA® and ENDURA® processing platforms available from Applied Materials, Inc. of Santa Clara, Calif.
In these cluster tools, a central transfer is typically surrounded by one or more processing chambers, at least one load lock chamber and sometimes a dedicated orientation chamber. The processing chambers are generally utilized to perform various processing steps such as etching, physical vapor deposition, chemical vapor deposition, ion implantation, lithography and the like. Processed and unprocessed substrates are housed in a substrate storage cassette disposed in a factory interface coupled to the load lock chamber. The load lock chamber is isolated from the factory interface and the transfer chamber by slit valves. Substrates enter the transfer chamber from the substrate storage cassettes one at a time through the load lock. The substrate is first positioned in the load lock after the substrate is removed from the cassette. The load lock is then sealed and pumped down to match vacuum the operating environment of the substrate transfer chamber. The slit valve between the load lock and transfer chamber is then opened, allowing the substrate transfer robot to access the substrates disposed in the substrate storage cassette. In this fashion, substrates may be transferred into and out of the transfer chamber without having to repeatedly re-establish transfer chamber vacuum levels after each substrate passes through the load lock.
Some processes such as etching and ion implantation require that the substrate have a particular orientation. Typically, substrates include indicia, such as notches or flats on their perimeters in pre-defined locations, that is typically indicative of the orientation of the substrate. Such notches are used as a reference point when orientation of the substrate is required.
Typically, orientation of the substrate occurs in the orientation chamber. The orientation chamber generally includes a platform for rotating the substrate and a sensor for detecting the notch or flat on the substrate's perimeter. For example, the platform disposed in the orientation chamber supports the substrate. A shaft is coupled between the platform and a stepper or servo motor to controllably rotate the substrate. A light source is positioned in the orientation chamber near the edge of the substrate and is directed across the substrate's edge to a sensor. The light source is normally blocked by the substrate's perimeter as the perimeter rotates. As the indicia (e.g., the notch or flat) rotates to a position between the light source and sensor, the light beam passes therethrough and impinges on the sensor. The sensor, in response to the impingement of the light beam, indicates the position of the notch, which accordingly, is indicative of the angular orientation of the substrate. Once the position of the notch is determined, the motor is able to rotate the platform and place the notch in a pre-determined angular position that can be referenced throughout the cluster tool and associated chambers.
Although the use of a dedicated orientation chamber coupled to the cluster tool has traditionally provided a robust process for determining the orientation of a substrate, the demand in the semiconductor industry for reduced cost of tool ownership and increased substrate throughput has made the use of a dedicated orientation chamber undesirable. For example, a dedicated orientation chamber increases the cluster tool hardware and software cost. Moreover, the orientation chamber may utilize a position on the cluster tool that could be allocated to an additional process chamber. Additionally, the use of a dedicated orientation chamber requires a time expenditure that is not directly related to processing. For example, time is spent transferring the substrate into the orientation chamber, clearing the robot arm from the orientation chamber, spinning (i.e., orientating) the substrate and retrieving the substrate. This time is significant as the orientation process takes about six to fourteen seconds to execute.
Therefore, there is a need for an improved method and apparatus for transferring a substrate.